[Assets] Switch from implicit project to explicit project if necessary (

fixes #442)

sources/assets/Xenko.Core.Assets/Package.cs

@@ -274,6 +274,23 @@ public bool IsDirty
         [DataMemberIgnore]
         public string RootNamespace { get; private set; }
 
+        [DataMemberIgnore]
+        public bool IsImplicitProject
+        {
+            get
+            {
+                // To keep in sync with LoadProject() .csproj
+                // Note: Meta is ignored since it is supposedly "read-only" from csproj
+                return (AssetFolders.Count == 1 && AssetFolders.First().Path == "Assets"
+                    && ResourceFolders.Count == 1 && ResourceFolders.First() == "Resources"
+                    && OutputGroupDirectories.Count == 0
+                    && ExplicitFolders.Count == 0
+                    && Bundles.Count == 0
+                    && RootAssets.Count == 0
+                    && TemplateFolders.Count == 0);
+            }
+        }
+
         /// <summary>
         /// Adds an existing project to this package.
         /// </summary>

sources/assets/Xenko.Core.Assets/PackageSession.cs

@@ -385,6 +385,11 @@ private void DirectDependencies_CollectionChanged(object sender, NotifyCollectio
 
         protected override void SavePackage()
         {
+            // Check if our project is still implicit one
+            // Note: we only allow transition from implicit to explicit (otherwise we would have to delete file, etc.)
+            if (IsImplicitProject && Package.IsDirty && !Package.IsImplicitProject)
+                IsImplicitProject = false;
+
             if (!IsImplicitProject)
                 base.SavePackage();
         }